1. Field of the Invention
The present invention is directed to a solid polymer electrolyte fuel cell having a coolant circulation circuit.
2. Discussion of the Background Art
A conventional solid polymer electrolyte fuel cell of this kind, disclosed in U.S. Pat. No. 4,988,583, for maintaining the temperature of the cell at a desired or predetermined value, is illustrated in FIG. 12. As is there illustrated, the major surface of each of the plates PT is provided with a single continuous open-faced fluid flow channel P which traverses the central area of the plate surface in a serpentine manner. Coolant flows into an inlet port I, through the fluid flow channel P, and out from an outlet port O. The f low direction of the coolant is along the flow directions of fuel and air. Such a design structure is conventional in most solid polymer electrolyte fuel cells.
In the foregoing structure, gradients arise in the fuel (air) flow direction, for the gas composition, pressure, temperature, and humidity. However, the temperature gradient of coolant at the cell surface, which results mainly from heat exchange between the coolant and the reaction waste heat, is not undesired or unsuitable for the local pressure, temperature, and humidity required by both the fuel electrode and air electrode. But the coolant temperature gradient at the cell surface is linear, whereas it should be nonlinear in order for the current density distribution of the cell to be uniform. Thus, along the cell surface, the gas conditions at the fuel and air electrodes becomes uneven.
The aforementioned uneven gas conditions of the fuel and air results in the in-cell resistance varying widely, and so the current density on the cell surface varies widely. Such variation of the current density causes a scattering of the in-cell reaction heat distribution, which makes it difficult to establish heat management and water management, whereby the thermal hysteresis difference between catalysts and the thermal hysteresis difference between ion exchange membranes become large. Thus, the life of each of the catalysts and each of the ion exchange membranes is reduced.
In view of the foregoing circumstances, there is a need for an optimal fluid flow channel which is free from the foregoing drawbacks.
It is, therefore, a primary object of the present invention to provide a solid polymer electrolyte fuel cell which meets such a need.
In order to attain the foregoing and other objects, according to a first aspect thereof the present invention provides a solid polymer electrolyte fuel cell having a coolant circulation circuit, the solid polymer electrolyte fuel cell comprising a cell part having a cell surface; a coolant flow field plate having a surface positioned opposed to the cell surface; an open-faced coolant flow channel formed in a region of the surface of the coolant flow field plate, the open-faced coolant flow channel being divided into a plurality of divisional passages; a coolant inlet provided port at one end of each of the divisional passages; and a coolant outlet port provided at the other end of each of the divisional passages.
In accordance with the first aspect of the present invention, the regions defined by the respective divisional passages can differ in temperature gradient.
According to a second aspect of the present invention, the coolant outlet port of an upstream one of the divisional passages is adjacent the coolant inlet port of a downstream one of the divisional passages in a direction of coolant flow.
In accordance with the second aspect of the present invention, the introduction of the coolant f an upstream side divisional passage into a downstream side divisional passage becomes easier.
A third aspect of the present invention is to provide a solid polymer electrolyte fuel cell wherein the divisional passages are connected in series.
In accordance with the third aspect of the present invention, it becomes possible to establish a temperature pattern wherein the different temperature gradients continue.
In accordance with a fourth aspect of the present invention, a heat exchanger is interposed in a flow path of the coolant between the coolant outlet port of the upstream one of said divisional passages and the coolant inlet port of the downstream one of said divisional passages.
In accordance with the fourth aspect of the present invention, the heat exchanged or temperature controlled coolant is introduced into the downstream side divisional passage, which makes it possible to adjust the temperature gradients at the cell surface in an arbitrary fashion.
A fifth aspect of the present invention is to provide a solid polymer electrolyte fuel cell according to the third aspect, wherein a flow rate regulator is interposed in a flow path of the coolant between the coolant outlet port of the upstream one of said divisional passages and the coolant inlet port of the downstream one of said divisional passages.
In accordance with the fifth aspect of the present invention, the heat exchanged or temperature controlled and amount-adjusted coolant is introduced into the downstream side divisional passage, which makes it possible to establish non-linear temperature gradients at the cell surface in an arbitrary fashion.
In accordance with a sixth aspect of the present invention, a flow rate regulator and a heat exchanger are interposed in a flow path of the coolant between the coolant outlet port of the upstream one of said divisional passages and the coolant inlet port of the downstream one of said divisional passages, wherein the heat exchanger is disposed between the flow rate regulator and the coolant inlet port of the downstream one of said divisional passages.
In accordance with the sixth aspect of the present invention, the amount-adjusted coolant is introduced into the downstream side divisional passage, which makes it possible to adjust the non-linear temperature gradients at the cell surface in an arbitrary fashion. In addition, excess local drying or wetting at each of the fuel and air electrodes can be restricted, which makes it possible to establish a uniform in-cell resistance and an even distribution of the current density at the cell surface.
In accordance with a seventh aspect of the present invention, a flow rate regulator and a heat exchanger are interposed in a flow path of the coolant between the coolant outlet port of the upstream one of said divisional passages and the coolant inlet port of the downstream one of said divisional passages, wherein the heat exchanger and the flow rate regulator are arranged in parallel.
In accordance with the seventh aspect of the present invention, the heat-exchanged amount-adjusted coolant is introduced into the downstream side divisional passage, which makes it possible to adjust the nonlinear temperature gradients at the cell surface in an arbitrary fashion. In addition, excess local drying or wetting at each of the fuel and air electrodes can be restricted, which makes it to establish a uniform in-cell resistance and an even distribution of the current density at the cell surface.